1. Field of the Invention
This invention relates to a karaoke CD system, more particularly to a karaoke CD format and a device for processing audio signals utilizing the karaoke CD format which provides a user with selective reproduction of the voice of a player.
2. Description of Related Art
As shown in FIG. 1, a general disc data layout of a karaoke CD includes lead in/lead out areas 1 and 6 formed at the lead in and lead out of the CD for encoding CD-ROMXA data containing empty sectors of mode 2/form 2 therein, and program areas 2, 3, 4, and 5.
The program areas include a volume descriptor area 2 formed next to the lead in area 1 containing the path name of a CDI application program described in compact disc bridge system description. The basic data area 3 is for recording the title of a song, the name of the singer, the composer of the song, and the songwriter. The CDI application program area 4 is for recording an application program required for converting into compact disc bridge system description which will facilitate the operation of a disc in CD-RTOS (Real Time Operating System) in a CD-I/FMV player. The MPEG data area 5 is for recording MPEG (Moving Picture Experts Group) video and audio data.
The lead in area 1 has records of the number of songs, the period of time of each song and total period of time, and the lead in part and index part of each song. The lead out area 6 has record of the end of the program.
As shown in FIG. 2, a conventional karaoke CD system includes a first demodulation part 11 for demodulating EFM (Eight to Fourteen Modulation) signals. A second modulation part 12 for demodulating signals recorded in interleaved sectors for a CD-ROM upon receiving signals from the first demodulation part 11. A CPU 16 for demultiplexing system flow on receiving signals from the second demodulation part 12. A first, and a second memory 17 and 18 for storing video and audio data received from the CPU 16 respectively. A MPEG video decoder 19 and a MPEG audio decoder 20 for decoding MPEG video signals and MPEG audio signals of the video and audio data stored in the first and the second memories 17 and 18 respectively. A STC (System Time Clock) 23 for clocking the system time under the control of the CPU 16. A video and audio signal processing part 13 having a video presentation part 21 for comparing the STC of the STC part 23 to PTS (Presentation Time Stamps) in the bit stream received from the MPEG video decoder 19. An audio presentation part 22 for comparing the STC of the STC part 23 to PTS (Presentation Time Stamps) in the bit stream received from the MPEG audio decoder 20. A control part 10 for controlling both the first and the second demodulation parts 11 and 12 and for controlling the video and audio signal processing part 13 according to a key signal applied thereto. A Digital-to-Analog (D/A) converter 14 for converting the video signal received from the video presentation part 21 and outputting the converted signal to a monitor under the control of the control part 10, and a D/A converter 15 for converting the audio signal received from the audio presentation part 22 and applying the converted signal to a speaker under the control of the control part 10.
The interleaving of a conventional MPEG video and MPEG audio sectors is as shown in FIG. 3.
Since the quantity of MPEG video data is much greater than the quantity of MPEG audio data, an MPEG audio sector A is periodically positioned in between MPEG video sectors V. For example, one MPEG audio sector A may be present in every four MPEG video sectors V.
Shown in Table 1 is the audio channel encoding, which is to be explained in detail hereinafter.
TABLE 1Stereo ProgramSpecial Music ProgramCH 0Leftmono without vocalCH 1Rightmono with vocal
The karaoke CD format includes a stereo music program having a left audio channel for encoding on MPEG audio channel 0 and a right audio channel for encoding on MPEG audio channel 1, and a special music program having one channel for encoding music accompaniment sound without vocal and the other channel for encoding music accompaniment sound with vocal.
Operation of the conventional karaoke CD system is to be explained hereinafter.
The karaoke data is read in through a pick-up, having EFM demodulated and CD errors corrected through the first demodulation part 11 which is an EFM/CIRC (Cross Interleave Read Solomon Code) decoder. The data interleaved at encoding is demodulated through the second demodulation part 12 which is a CD-ROM decoder. The data is divided into audio data and video data through the video and audio signal processing part 13 under the demultiplexing operation of the CPU 16 and applied to the MPEG video decoder 19 and MPEG audio decoder 20 through the first and the second memories 17 and 18 respectively.
The MPEG video decoder 19 and the MPEG audio decoder 20, restore the compressed data, and compare the STC from the STC part 23 to the PTS in the restored data to control the presentation time of the data.
However, such a conventional karaoke-CD system has the disadvantage of being unable to obtain stereophony sound in the case where music without vocal and music with vocal of a specific music program is carried on the first channel (Left) and the second channel (Right).